The invention relates to an internal combustion engine system, a combined compressor and expander for an internal combustion engine system, a method for an internal combustion engine system, a computer program, a computer readable medium, and a control unit.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment, e.g. working machines. The invention can also be applied to cars. Although, the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle type.
It is known that internal combustion engines with two stages of compression and two stages of expansion, e.g. by a compressor, a combustor and an expander, may provide for reaching very high pressures and for extracting more energy from the fuel. However, a highly efficient vehicle engine may have very cool tailpipe exhaust, which may prevent or reduce the efficiency of exhaust treatment processes provided by exhaust treatment devices such as catalytic converters of various types. For certain processes, e.g. selective catalytic reduction SCR), it is possible to compensate for low temperatures by providing large exhaust treatment devices; however, this will increase the weight and volume of the engine system, which may be a problem, particularly in vehicles, where often there are demanding space requirements.
US2010300385 discloses an engine with two stages of compression and two stages of expansion, where an oxidation catalyst is positioned between a power cylinder and an expander cylinder. However, for many exhaust treatment processes, e.g. SCR, such a location provides temperatures which are too high.
It is desirable to reduce emissions from an internal combustion engine with a compressor, a combustor and an expander. It is also desirable to provide an internal combustion engine system with a compressor, a combustor and an expander, which provides an effective treatment of exhaust gases, while avoiding large increases of the volume and/or weight of the engine system.
According to an aspect of the invention, an internal combustion engine system is provided comprising    at least one combustor, and    a first expander arranged to receive exhaust gases from at least one of the at least one combustor, and to expand and extract energy from the exhaust gases,    characterized in that the system comprises a second expander arranged to receive exhaust gases from the first expander, and to expand and extract energy from the exhaust gases.
Herein, the engine system is understood as comprising an internal combustion engine, in turn comprising the combustor, the first expander and the second expender.
The invention provides for the expansion of the engine system being done in at least three steps. In turn this provides for providing two different temperature ranges, one upstream of the first expander, and one between the first and second expanders. Thereby the engine system may provide a plurality of simultaneous temperature ranges, each suitable for one or more respective exhaust treatment processes.
Thus, the system may advantageously be provided with an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases, and to deliver the processed exhaust gases to the second expander. Thereby, it is possible to provide the exhaust treatment device in a form, e.g. as a selective catalytic reduction (SCR) catalyst, requiring a temperature range which is lower than the temperature range upstream of the first expander. In particular, the temperature range between the expanders may be kept higher than in a portion of an exhaust system communicating directly with the atmosphere, e.g. a vehicle tail pipe; however, the temperature range between the expanders may be kept lower than between the combustor and the first expander.
In a vehicle, where the exhaust treatment device is an SCR catalyst, the position in the elevated temperature between the expanders allows for a smaller SCR than if it would be positioned in the tailpipe. This makes it possible to provide the SCR catalyst as a cheap catalyst for nitrogen oxide (NOx) reduction in a temperature range 300-450 C with a high conversion. Specifically, the catalyst size may be reduced, which reduces the volume and weight of the engine system.
Advantageously, the system comprises an injector arranged to inject reductant for the exhaust treatment device, upstream of the first expander or into the first expander. Thereby, the timing and/or duration of the reductant injections by the injector may be coordinated with the actuation of an inlet valve of the first expander. This will provide good mixing of the reductant with the exhaust gases. It is understood that the reductant may be a solution of urea or another reductant useful for lowering particulant emissions and/or nitrogen oxide emissions from the engine. The reductant may a solution of organic and inorganic nitrogen compounds.
As also discussed below, where the reductant comprises urea, the first expander may promote thermolysis of the urea to decompose it into isocyanate and ammonia before it reaches the SCR catalyst. Thereupon the isocyanate may be processed by hydrolysis to provide ammonia. Injecting the reductant upstream of the first expander or into the first expander may support the thermolysis and the hydrolysis, since these processes will be enhanced by the heat therein. Advantageously, where the first expander is a piston expander, the injector may be arranged to inject reductant for the exhaust treatment device, into the first expander and onto the piston of the first expander, e.g. onto a piston crown of the piston. Thereby, the thermolysis and the hydrolysis may be particularly supported by heat stored in the piston, e.g. in a top section of the piston. For example, the heat stored in the piston crown of the piston may support the thermolysis and the hydrolysis.
Preferably, the system comprises in addition to said exhaust treatment device a pre-expander exhaust treatment device arranged to receive exhaust gases from the combustor, to provide an exhaust treatment process to the exhaust gases, and to deliver processed exhaust gases to the first expander. The pre-expander exhaust treatment device may comprise an oxidation catalyst, and/or a particulate filter. Where both are provided, the particulate filter may be located downstream of the oxidation catalyst. The system may further be arranged so that during an operation thereof, the pre-expander exhaust treatment device presents a temperature within the range of 550-1300° C., preferably within the range of 550-1100° C., e.g., within the range of 550-800° C. The pre-expander exhaust treatment device temperature may vary depending of the engine load. At full engine load, the pre-expander exhaust treatment device temperature may be e.g. 900-1100° C. Thereby, an advantageous distribution of exhaust treatment devices along the path of the exhaust gases may be provided, giving different temperatures which are each optimized for the respective exhaust treatment device.
It is understood that depending on the provision of the pre-expander exhaust treatment device, the first expander is arranged to receive processed or unprocessed exhaust gases from the combustor. Exhaust gases are herein understood as being processed if they are received from an exhaust treatment device.
In some embodiments, e.g. where there is no pre-expander exhaust treatment device, the first expander may be arranged to utilize pressure pulses in the exhaust gases received from the at least one of the at least one combustor, to increase the power output of the first expander.
Herein, the engine system is understood as comprising the engine, in turn comprising the combustor, the first expander and the second expender, and the engine system is understood as comprising the engine, and, where provided, the pre-expander exhaust treatment device, and the post-expander exhaust treatment device.
The invention is particularly advantageous where the system comprises a crankshaft, and the combustor comprises a piston arranged to reciprocate in a cylinder, and to drive the crankshaft. It is understood that the system may comprise a plurality of combustors, each comprising a piston arranged to reciprocate in a respective cylinder, whereby the pistons are all arranged to drive the crankshaft.
The first expander is preferably a piston expander arranged to drive the crankshaft with the extracted energy. Similarly, the second expander is preferably a piston expander arranged to drive the crankshaft with the extracted energy. The system may comprise at least one compressor, which may be a piston compressor, arranged to be driven by the crankshaft. Thus, the invention may be advantageously implemented in a multistage compression and expansion engine where the compressor(s) and the expanders are connected to the crankshaft. Such a connection may be direct or indirect, as exemplified below. Thereby, the system may present a high efficiency. Typically, the expanders may provide 30-50%, e.g. 40%, of the total power of the engine, and the compressor(s) may take 10-20% of the total power of the engine.
It should be noted however that within the scope of the claims, the first expander may be of a type other than a piston expander. For example, the first expander may be a turbine. The turbine may be arranged to drive a compressor for compressing air for the combustor, or it may be arranged to drive the crankshaft with the extracted energy. Similarly, the second expander may be of a type other than a piston expander. For example, the second expander may be a turbine. The turbine may be arranged to drive a compressor for compressing air for the combustor, or it may be arranged to drive the crankshaft with the extracted energy.
In some embodiments, where the system comprises a compressor arranged to compress air for at least one of the at least one combustor, the second expander may comprise a turbine arranged to drive the compressor or an additional compressor. Thereby, the system may be provided with a high power density. Where an additional compressor is provided, it may be arranged to deliver compressed air to said compressor arranged to compress air for at least one of the at least one combustor. Thus, an advantageous three step compression may be provided.
In an advantageous embodiment, where the system comprises a crankshaft, and a compressor arranged to compress air for at least one of the at least one combustor, the compressor and one of the first expander and the second expander are integrated so as to share a piston which is connected to the crankshaft. Thereby, the compressor and the one of the first expander and the second expander may form a combined compressor and expander whereby the piston is arranged to reciprocate in a shared cylinder, the combined compressor and expander being arranged to admit air to the shared cylinder, on a first side of the piston, and to compress the air, by means of the piston, for the combustor, the combined compressor and expander further being adapted to admit the exhaust gases, received by the one of the first expander and the second expander, to the shared cylinder, on a second side of the piston, to expand the exhaust gases by means of the piston.
The shared piston makes it possible to use the urge of the piston by the expander to deliver, in addition to power to the crankshaft, power for the air compression in a direct manner. More specifically, the exhaust gases may provide a direct pressure on the shared piston in turn serving to directly exert a direct pressure on the air. Thereby, mechanical losses for the transfer of this energy is substantially eliminated. Also, compared to providing the compressor and expander separately, the compressor and expander combination results in a reduced number of parts, since the piston and the cylinder are shared, thereby reducing the volume, weight, complexity and cost of the engine system.
Preferably, the combustor comprises an exhaust valve, herein also referred to as an outlet valve, the system further comprising a variable valve timing mechanism arranged to actuate the exhaust valve.
Preferably, the first expander comprises an expander inlet valve, the system further comprising an expander variable valve timing mechanism arranged to actuate the expander inlet valve. Thereby a possibility is provided to advantageously adjust the swallowing capacity of the first expander as exemplified below. For example, adjusting the temperature of an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases, and to deliver the processed exhaust gases to the second expander, may be done by adjusting the swallowing capacity of the first expander.
In some embodiments, the first expander is a variable-geometry turbine, e.g. of a variable-geometry turbocharger (VGT). This provides an alternative possibility to adjust the swallowing capacity of the first expander.
Preferably, the first expander comprises an expander exhaust valve, herein also referred to as an outlet valve, the system further comprising an expander variable valve timing mechanism arranged to actuate the expander exhaust valve. As exemplified below, this allows for an advantageous manner of controlling the temperature of the post-expander exhaust treatment device. For example, thereby the first expander may be used for increasing the temperature, e.g. at a cold start event, of an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases, and to deliver the processed exhaust gases to the second expander. For example, by advancing an opening event of the expander exhaust valve, so that it opens before a bottom dead center (BDC) position of the piston in the first expander, the expander exhaust valve may be opened before the expansion in the first expander is completed. Thereby, heat remaining in the gases in the first expander may be used to increase the exhaust treatment device temperature. In addition, the exhaust valve may be closed at the BDC position, and opened at a position after the BDC position, e.g. 45 crankshaft degrees after the BDC position. Thereby, a recompression of the gases in the first expander may occur, and the heat generated thereby may be used to increase the exhaust treatment device temperature.
In some embodiments, the first expander may comprise a hydrolysing reactor. This is particularly advantageous where the system comprises, as described above, an injector arranged to inject reductant for an exhaust treatment device, upstream of the first expander or into the first expander. Where the reductant comprises urea, e.g. where the exhaust treatment device is an SCR catalyst, the first expander may promote thermolysis of the urea to decompose it into isocyanate and ammonia before it reaches the catalyst. Thereupon the isocyanate may be processed by hydrolysis to provide ammonia. Injecting the reductant upstream of the first expander or into the first expander may support the thermolysis and the hydrolysis, since these processes will be enhanced by the heat therein. The hydrolysing reactor may involve as discussed above an injector arranged to inject reductant for an exhaust treatment device, into the first expander and onto a piston of the first expander. The first expander may also provide a beneficial thorough mixing of the reductant with the exhaust gases.
It should be noted that in some embodiments, an injector may be arranged to inject reductant downstream of the first expander. Thereby, an exhaust treatment device such as an SCR catalyst may be provided downstream of the second expander. This may provide a relatively long flow path for the reductant, past the second expander, to allow a good mix of the reductant and the exhaust gases.
According to another aspect of the invention, an internal combustion engine system is provided comprising    at least one combustor, and    an expander arranged to receive exhaust gases from at least one of the at least one combustor, and to expand and extract energy from the exhaust gases,    characterized in that the system comprises an exhaust treatment device arranged to receive exhaust gases from the expander, and to process the received exhaust gases,    and that the system comprises an injector arranged to inject reductant for the exhaust treatment device, upstream of the expander or into the expander.
The exhaust treatment device may be a selective catalytic reduction (SCR) catalyst. Thereby, by injecting reductant upstream of the expander or into the expander, advantage may be taken of a higher temperature of the exhaust gases before they are subjected to the expansion of the expander, to provide thermolysis of the reductant, e.g. where the reductant is provided in the form of urea, to provide ammonia for the process in the exhaust treatment device. In addition, such a system allows for the expander to form a mixing volume for the reductant, which in turn allows for reducing the volume downstream of the expander. Thereby, space can be saved which may be critical in a vehicle application.
Preferably, the injector is arranged to inject reductant for the exhaust treatment device, into the expander and onto a piston of the expander. Advantages thereof have been mentioned above.
The invention also provides a combined compressor and expander for an internal combustion engine system, comprising    a cylinder,    a piston adapted to be connected to a crankshaft of the engine system, and arranged to reciprocate in the cylinder, the combined compressor and expander being adapted to admit air to the cylinder, on a first side of the piston, and to compress the air by means of the piston for a combustion process of the engine system,    the combined compressor and expander further being adapted to admit exhaust gases, obtained from a combustion process of the engine system and/or an exhaust gas treatment process of the engine system, to the cylinder, on a second side of the piston, to expand the exhaust gases by means of the piston to extract, energy from the expanded exhaust gases.
Thereby the compressor and expander are integrated with each other, and one cylinder and piston combination may be used for both compression and expansion. The power extracted by the expander will contribute to driving the crankshaft and/or to compress the air. The air compression process may be driven by the crankshaft and/or the exhaust gas expansion. As mentioned, the compressor and expander combination results in a reduced number of parts, since the piston and the cylinder are shared, thereby reducing the volume, weight, complexity and cost of the engine system.
According to another aspect of the invention, a method for an internal combustion engine system is provided comprising    at least one combustor, arranged to combust air and fuel,    a first expander arranged to receive exhaust gases from at least one of the at least one combustor, and to expand and extract energy from the exhaust gases,    a second expander arranged to receive exhaust gases from the first expander, and to expand and extract energy from the exhaust gases, and    an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases, and to deliver the processed exhaust gases to the second expander, the method comprising adjusting the swallowing capacity of the first expander to control the temperature of the process in the exhaust treatment device.
The swallowing capacity of the first expander is understood as the capacity of the first expander to accept gases and pass them on to a conduit downstream of the expander. The swallowing capacity of the first expander is proportional to the mass flow through the first expander at a given intake pressure and temperature. A decreased swallowing capacity provides an increased strangulation of the gas flow. A decreased swallowing capacity of the first expander provides an increased pressure drop across the first expander. A decreased swallowing capacity may provide an increased first expander expansion ratio as understood by the pressure drop across the first expander.
By said method, an advantageous and reliable manner of controlling the temperature of the process in the exhaust treatment device is provided. For example, the method may comprise increasing the temperature of the exhaust treatment device by increasing the swallowing capacity of the first expander, and decreasing the temperature of the exhaust treatment device by decreasing the swallowing capacity of the first expander.
The first expander may be arranged to receive the exhaust gases by means of an expander inlet valve, an expander variable valve actuation mechanism being arranged to actuate the expander inlet valve, wherein adjusting the swallowing capacity of the first expander comprises adjusting the expander variable valve actuation mechanism. Thereby, the temperature control may be effected by means of readily available assemblies. The expander variable valve actuation mechanism may be e.g. a variable valve timing mechanism. The expander variable valve actuation mechanism may be of any suitable type, e.g. involving cam switching, cam phasing, an oscillating cam, an eccentric cam drive, a three-dimensional cam lobe, a two shaft combined cam lobe profile, a coaxial two shaft combined cam lobe profile, a helical camshaft, or a camless mechanism.
The method may comprise increasing the swallowing capacity of the first expander by delaying a closing event of the expander inlet valve, and decreasing the swallowing capacity of the first expander by advancing the closing event of the expander inlet valve. For example, in two stroke cycles of the first expander, the expander inlet valve may be controlled so as to open at a top dead center (TDC) position of the piston in the first expander, and so as to close at 25 crankshaft degrees after the TDC position. The swallowing capacity may be increased by delaying the inlet valve closing, e.g. to 30 crankshaft degrees after the TDC position. The swallowing capacity may be decreased by advancing the inlet valve closing, e.g. to 20 crankshaft degrees after the TDC position.
Preferably, the first expander is arranged to expel the exhaust gases by means of an expander exhaust valve, the expander variable valve actuation mechanism being arranged to actuate the expander exhaust valve, the method comprising controlling the expander variable valve actuation mechanism so as to adjust the expander exhaust valve to minimize the pressure difference across the expander exhaust valve at an opening event of the expander exhaust valve, and/or to minimize the pressure difference across the expander inlet valve at an opening event of the expander inlet valve. The adjustment of the expander exhaust valve to minimize the pressure difference across the expander inlet valve at an opening event of the expander inlet valve may be done by suitable control of an expander exhaust valve closing event, to provide a degree of recompression in the expander.
According to another aspect of the invention, a method for an internal combustion engine system is provided comprising    at least one combustor, arranged to combust air and fuel,    a first expander arranged to receive exhaust gases from at least one of the at least one combustor, and to expand and extract energy from the exhaust gases,    a second expander arranged to receive exhaust gases from the first expander, and to expand and extract energy from the exhaust gases, and    an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases, and to deliver the processed exhaust gases to the second expander, the method comprising adjusting the swallowing capacity of the second expander to control the temperature of the process in the exhaust treatment device.
Similarly to the first expander, the swallowing capacity of the second expander is understood as the capacity of the second expander to accept gases and pass them on to a conduit downstream of the second expander. The swallowing capacity of the second expander is proportional to the mass flow through the second expander at a given intake pressure and temperature. A decreased swallowing capacity provides an increased strangulation of the gas flow. A decreased swallowing capacity of the second expander provides an increased pressure drop across the second expander. A decreased swallowing capacity may provide an increased second expander expansion ratio as understood by the pressure drop across the second expander.
Thereby, a further advantageous manner of controlling the exhaust treatment device temperature is provided. Increasing the temperature of the exhaust treatment device may be done by decreasing the swallowing capacity of the second expander, and decreasing the temperature of the exhaust treatment device may be done by increasing the swallowing capacity of the second expander.
Adjusting the swallowing capacity of the first expander and/or the second expander may advantageously be done in dependence on a rotational speed of the engine system and/or a requested torque for the engine system. For example, with a decreasing rotational speed of the engine system, the swallowing capacity of the first expander may be increased, and/or the swallowing capacity of the second expander may be decreased. As another example, with an increasing requested torque, providing an increased exhaust gas temperature, the swallowing capacity of the first expander may be decreased and/or the swallowing capacity of the second expander may be increased.
Preferably, the method comprises increasing the temperature of the exhaust treatment device by increasing the swallowing capacity of the first expander and decreasing the swallowing capacity of the second expander, and decreasing the temperature of the exhaust treatment device by decreasing the swallowing capacity of the first expander and increasing the swallowing capacity of the second expander. Thereby, a particularly effective temperature control is provided by combined adjustments of the first and second expander swallowing capacities. However, in some embodiments, the temperature of the exhaust treatment device is adjusted by adjusting the swallowing capacity of the first expander while keeping the swallowing capacity of the second expander constant. In further embodiments, the temperature of the exhaust treatment device is adjusted by adjusting the swallowing capacity of the second expander while keeping the swallowing capacity of the first expander constant. As suggested above, the first and second expanders may be of any suitable type, and they may be of the same type or of dissimilar types. The first expander may be a piston expander with a variable valve actuation mechanism or a variable-geometry turbine. The second expander may be a piston expander with a variable valve actuation mechanism or a variable-geometry turbine.
Preferably, the method comprises determining a temperature of the exhaust gases and, with an increasing exhaust gas temperature, decreasing the swallowing capacity of the first expander and increasing the swallowing capacity of the second expander, and, with a decreasing exhaust gas temperature,increasing the swallowing capacity of the first expander and decreasing the swallowing capacity of the second expander. Thereby, an accurate temperature control may be provided.
According to another aspect of the invention, a method for an internal combustion engine system is provided comprising a combustor arranged to combust air and fuel, an expander arranged to receive, expand and extract energy from exhaust gases from the combustor, and to expel the exhaust gases from the expander by means of an expander exhaust valve, and an exhaust treatment device arranged to receive the expelled exhaust gases from the expander and to process the exhaust gases, the method comprising controlling the expander exhaust valve to control the temperature of the process in the exhaust treatment device.
Said control of the expander exhaust valve may comprise controlling the temperature of the process in the exhaust treatment device to be within the range of 300-450° C. The method provides an effective manner of controlling the temperature of the exhaust treatment device, for keeping it within a range that is beneficial to the process therein. The distribution of exhaust treatment devices on both sides of the expander, as exemplified elsewhere herein, along with the control of the expander exhaust valves, provides an advantageous way of adapting the temperatures along the path of the exhaust gases for optimizing the processes in the exhaust treatment devices.
According to another aspect of the invention, a method for an internal combustion engine system is provided comprising a combustor arranged to combust air and fuel, an expander arranged to receive, expand and extract energy from exhaust gases from the combustor, the expander comprising an inlet valve, and an exhaust treatment device arranged to receive the exhaust gases from the expander and to process the exhaust gases, the method comprising injecting reductant for the exhaust treatment device upstream of the expander or into the expander,    controlling the expander inlet valve to allow exhaust gases into the expander,    wherein the timing and/or the duration of said reductant injection is coordinated with said control of the expander inlet valve so as for the reductant and the exhaust gases to mix in the expander.
It is understood that an injector may be arranged for said reductant injection. The method will provide good mixing of the reductant with the exhaust gases. Said reductant injection is preferably provided so that the injected reductant flows past the open expander inlet valve. Preferably, the reductant injection is commenced simultaneously with or after the opening of the expander inlet valve has commenced, and the reductant injection is terminated simultaneously with or before the closing of the expander inlet valve has been finalized.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.